Our laboratory is currently characterizing in vitro the functional activity of common polymorphisms of type-2 deiodinase gene. In order to achieve this goal, we have established a cell culture-based type-2 deiodinase expression system. Standard biochemistry methods are utilized for the enzymatic activity assay; protein/protein and nucleic acids/protein interactions are tested by immunoprecipitation and mobility shift assay. Very recently, a common polymorphism in the 5UTR region of the DIO2 gene (258 A/G DIO2) has been associated with a shift in the ratio of circulating T3/T4, suggesting an increased in the activity of the enzyme. Our data, consistent with the genotype/phenotype association studies, indicate that the 258 A/G DIO2 variant induces an increase in the transcription of the gene by displacing a putative repressor. Current efforts are aimed to characterize the putative repressor factor interacting with the polymorphism. Pathophysiology of thyrotoxicosis in patients affected by McCune-Albright syndrome. The clinical observation that McCune-Albright syndrome (MAS) is associated with hyperthyroidism with a shift in the ratio of circulating T3/T4 has led to the hypothesis that this finding could be at least in part explained by a an intra-thyroidal activation of the type-2 deiodinase gene. This is in keeping with the molecular pathology of MAS, i.e. activating mutations in GNAS1 gene resulting in ligand-independent inappropriately elevated levels of intracellular cAMP. We thus speculated that activation of the cAMP-driven deiodinase type-2 gene could explain at least in part these findings. Our in vitro and ex-vivo data indicate that, consistent with our experimental hypothesis, the type-2 deiodinase is constitutively activated in MAS. Thyroid hormone action on adipocytes. In order to study the interaction of thyroid hormones, other ligands and genetic background on the adipocyte metabolism from samples obtained from subcutaneous adipose tissue biopsies, we are currently performing preadipocytes isolation. Preadipocytes are then expanded and, after differentiation, characterized both transcriptional and biological activity.